1. Field of the Invention
The present invention relates to the field of semiconductor substrate processing equipment. More particularly, the present invention relates to an improved support member adapted for vacuum chucking of a substrate thereto and delivering a purge gas to the edge of a substrate supported thereon.
2. Background of the Related Art
In the fabrication of integrated circuits, equipment has been developed to automate substrate processing by performing a sequence of processing steps on a substrate without removing the substrate from a vacuum environment, thereby reducing transfer times and contamination of substrates. Such a vacuum system has been disclosed, for example, by Maydan et al. in U.S. Pat. No. 4,951,601, in which a plurality of processing chambers are connected to a central transfer chamber. A robot disposed in the central transfer chamber passes substrates through slit valve openings formed in the various connected processing chambers and retrieves the substrates after processing in the chambers is complete.
The processing steps carried out in the vacuum chambers typically require the deposition or etching of multiple metal, dielectric and semiconductive film layers on the surface of a substrate. Examples of such processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), and etching processes. Although the present application primarily discusses CVD process chambers and systems, the present invention is equally applicable to other process chambers and systems.
CVD vacuum chambers are employed to deposit thin films on semiconductor substrates. Typically, a precursor gas is charged into a vacuum chamber through a gas manifold plate situated above the substrate, and the substrate is heated to process temperatures generally in the range of about 250xc2x0 C. to about 650xc2x0 C. The precursor gas reacts on the heated substrate surface to deposit a thin layer thereon.
In a typical process chamber, a support member, commonly formed of aluminum, ceramic, or other material, on which a substrate is mounted during processing is vertically movable in the chamber. A plurality of support fingers are also vertically movable by an elevator and extend through the support member to facilitate transfer of a substrate from a robot blade to the support member. Typically, the support member also acts as a heater plate that is heated by a resistive heating element located therein which provides sufficient heat to maintain the substrate at a desired process temperature. Further, a purge gas is delivered to a perimeter of the substrate to prevent deposition gases from contacting and depositing on the edge and backside of the substrate.
Substrate uniformity is dependent on uniform heating and uniform purge gas delivery, among other things. Various known methods and support member designs are employed in the prior art to ensure such uniformity. For example, to increase the heat transfer from the support member to the substrate, the substrate is typically adhered to the upper surface of the support member by a xe2x80x9cvacuum chuck.xe2x80x9d Typically, vacuum chucking is accomplished by applying a pressure differential between grooves formed in the upper surface of the support member and the process chamber. As shown in FIG. 1, the upper surface 12 of the support member 10 of a prior system includes a plurality of concentric grooves 14 formed therein which intersect a plurality of radial grooves 16. A vacuum supply communicates with the grooves 14, 16 through holes 18 disposed along the plurality of radial grooves 16 to supply a vacuum thereto. The plurality of radial grooves 16 extend to a diameter slightly less than the diameter of a substrate. Thus, the vacuum supply is able to create a low pressure environment under the substrate to chuck, or adhere, the substrate to the upper surface 12. Pulling the substrate tightly against the upper surface 12 of the support member 10 enhances the surface to surface contact and, therefore, the heat transfer therebetween.
The purge gas channels 20 of the support member 10 are shown in FIG. 1 by hidden lines 21. The gas channels 20 comprise a complicated labyrinth of interconnected passageways constructed by drilling from the edge of the support member 10 inward. The gas channels 20 lead to a plurality of holes 22 disposed around the perimeter of the upper surface of the support member 10 which provide outlets for a purge gas delivered to the substrate edge. The gas is delivered from a gas source (not shown) to the gas channels 20 though a gas delivery channel formed in a shaft (also not shown) of the support member 10.
One problem associated with current systems occurs as a result of cleaning the process chamber. Material, such as tungsten, is deposited not only on the substrate during the deposition process, but also onto all of the hot chamber and support member components. Because the adhesion of the deposited material to the chamber and the support member is poor, the material tends to flake off over time creating particles within the system that can damage the chamber, the substrates, and the product. As a result, the deposited material must be removed periodically to avoid particle generation and contamination of substrates. The removal of the material is typically accomplished utilizing a low power fluorine containing plasma. In the case of tungsten, NF3 is typically the cleaning gas of choice. The fluorine radicals of the low power NF3 plasma attack the deposited tungsten during cleaning. However, the fluorine radicals also react with the aluminum of the support member to create an aluminum fluoride layer on the heater surface. Typically, this layer of aluminum fluoride is only about 0.0004 to about 0.0006 inches in thickness and does not create any detrimental effects as long as the thickness of the material is uniform. However, the grooves 14, 16 shown in FIG. 1 generally have a rectangular cross sectional shape which forms square corners at the intersection of the grooves 14, 16. Empirical studies have shown that the aluminum fluoride has greater accumulation at the intersections of the grooves of support members. This added accumulation of aluminum fluoride creates xe2x80x9cpillars,xe2x80x9d or raised areas, of aluminum fluoride which may exceed 0.004 inches. The pillars prevent the substrate from fully contacting the upper surface of the support member and interfere with chucking of the substrate by causing backside pressure failure. Accordingly, the pillars cause local heat transfer anomalies affecting film uniformity. Additionally, the NF3 cleaning gas is drawn into contact with the substrate backside and into the vacuum channels which result in contamination of the substrate and chamber components.
Further, as the overall density of vacuum channels, purge gas channels, heating coils, etc., increases, cross-talk between these various features formed in the support member also increases. Thus, for example, the vacuum channels and the gas channels communicate with one another, thereby compromising the operability of the support member and resulting in defective substrates.
Additionally, purge gas delivered through gas channels 20 such as the ones shown in FIG. 1, often experience different effective pressures at various locations depending on which channel the gas traveled along. This pressure differential causes local xe2x80x9cburstsxe2x80x9d of gas at the substrate edge resulting in non-uniformity of the deposited film.
Therefore, there is a need to provide a support member that eliminates the problems associated with current support members and also provides for chucking of the substrate to the support member, uniform heating of the substrate, uniform gas delivery, and the elimination of ridges of aluminum fluoride and other undesirable contaminants. Preferably the support member may be utilized for various sized substrates, such as 200 mm and 300 mm substrates, and can be scaled to other size substrates as well.
The present invention generally provides a support member adapted to provide vacuum chucking. In one aspect, a support member having an upper surface having an outer, raised portion defining an inner, recessed portion is provided. The inner recessed portion is in fluid communication with a vacuum supply. The support member may include a plurality of raised support portions having one or more recessed portions adjacent thereto, the raised support portions having equal heights above the recessed portions. The transition between the raised portions and the recessed portions is gradual and the orifices formed by the holes extending through the upper surface of the substrate support are rounded to eliminate sharp edges and rapid changes in height at the upper surface.
In another aspect, a method of supporting a substrate on a support member is provided, comprising positioning the substrate on an upper surface of the support member, the upper surface having an outer raised portion defining an inner, recessed portion and one or more raised support portions defining a gradual transition surface extending from the inner, recessed portion, the transition surface having a slope of less than a rise to run ratio of 1 to 1; supporting the substrate on the outer, raised portion and the raised support portions; and applying a vacuum across the inner, recessed portion.